1. Field of the Invention
The present invention relates generally to a solid electrolytic capacitor including a capacitor element packaged with synthetic resin. It more particularly relates to a structure of a surface-mounting solid electrolytic capacitor of the type which is mounted on a printed circuit board or the like by soldering, and to a method of making the same.
2. Description of the Related Art
Generally, a surface-mounting solid electrolytic capacitor of the above-described type comprises a capacitor element sealed in a synthetic resin package, an anode lead terminal for electrical connection with an anode wire of the capacitor element, and a cathode lead terminal for electrical connection with a cathode film of the capacitor element, wherein both leads are exposed at the bottom surface of the package.
In the solid electrolytic capacitor having such a structure, the anode lead terminal and the cathode lead terminal do not project from the package. Therefore, as compared with a surface-mounting capacitor which has an anode lead terminal and a cathode lead terminal projecting from opposite sides of the package and bent toward the bottom surface of the package, the capacitor having the above-described structure is smaller in height and length and is therefore advantageous for size and weight reduction. However, the capacitor has the following problems.
For making such a capacitor, a capacitor element is mounted to an anode lead terminal and a cathode lead terminal arranged in the same plane so that the anode wire of the capacitor element projects toward the anode lead terminal, whereas a side surface of the capacitor element comes into close contact with the upper surface of the cathode lead terminal. Then, after the anode wire of the capacitor element is fixed to the anode lead terminal, whereas a cathode film of the capacitor element is fixed to the cathode lead terminal, the entirety is sealed in a synthetic resin package.
In mounting the capacitor element to the anode lead terminal and the cathode lead terminal arranged in the same plane, the capacitor element need be positioned at the center widthwise of the two lead terminals for decreasing the width of the solid electrolytic capacitor as a product.
Conventionally, the widthwise positioning is performed by an automatic feeding device for automatically feeding capacitor elements relative to the lead terminals. Therefore, for enhancing the positioning accuracy, it is inevitable to make the automatic feeding device more complicated, which leads to an increase in cost. Further, for enhancing the positioning accuracy, the feeding speed of the capacitor elements and hence the manufacturing speed cannot be increased. Conversely, if the manufacturing speed is increased, the accuracy of the widthwise positioning is deteriorated, making the resulting product large in width.
Moreover, when the capacitor element is mounted to the anode lead terminal and the cathode lead terminal arranged in the same plane so that one side of the capacitor element comes into close contact with the upper surface of the cathode lead terminal, the anode wire of the capacitor element is spaced above the anode lead terminal, forming a gap between the anode wire and the anode lead terminal.
Conventionally, to bridge the gap and electrically connect the anode wire to the anode lead terminal, the anode lead terminal or the anode wire is fixed, in advance, to a bolster made of a metal by welding for example, and the bolster is fixed to the anode wire or the anode lead terminal by welding for example. However, such an arrangement greatly increases the manufacturing cost.
It is, therefore, an object of the present invention to provide a structure of a solid electrolytic capacitor which is free from these problems and to provide a method of making such a capacitor.
A solid electrolytic capacitor according to the present invention comprises a capacitor element having an end surface provided with an anode wire projecting therefrom, a package formed of synthetic resin for entirely sealing the capacitor element, an anode lead terminal electrically connected to the anode wire of the capacitor element, and a cathode lead terminal kept in close contact with a side surface of the capacitor element, the package having a bottom surface at which the anode lead terminal and the cathode lead terminal are exposed. The anode lead terminal has an end portion directed toward the capacitor element and formed with an upwardly bent piece, the upwardly bent piece being formed with a positioning groove for receiving the anode wire.
Further, a method of making a surface-mounting solid electrolytic capacitor according to the present invention comprises the steps of preparing a lead frame formed with plural sets of anode lead terminals and cathode lead terminals each for constituting a solid electrolytic capacitor, upwardly bending a tip end of each anode lead terminal while forming a positioning groove at the tip end, mounting a capacitor element to each set of the anode lead terminal and the cathode lead terminal of the lead frame so that the anode wire of the capacitor element is fitted in the positioning groove of the anode lead terminal, whereas a side surface of the capacitor element comes into close contact with the cathode lead terminal, and forming an overall sealing package of synthetic resin followed by cutting into a plurality of solid electrolytic capacitors.
As described above, the end portion of the anode lead terminal directed toward the capacitor element is bent upward to provide a bent piece formed with a positioning groove and the anode wire of the capacitor element is fitted in the positioning groove. With this structure, when the capacitor element is mounted to the anode lead terminal and the cathode lead terminal, the upwardly bent piece completely bridges a conventionally formed gap between the anode wire and the anode lead terminal. Further, the capacitor element can accurately be positioned at the center widthwise of the anode lead terminal and the cathode lead terminal.
Therefore, according to the present invention, due to the accurate widthwise positioning, the resulting solid electrolytic capacitor as a product can be reduced in width, which leads to size and weight reduction of the product. Further, since the conventionally used metal bolster need not be provided, the manufacturing process is simple and can be performed at a high speed, which leads to a large decrease of the manufacturing cost.
Moreover, the provision of the fitting portion for the capacitor element in the cathode lead terminal at the portion for contacting the side surface of the capacitor element not only enhances the accuracy of the widthwise positioning of the capacitor element relative to the two lead terminals but also contributes to the reliable positioning of the capacitor element in parallel to the two lead terminals. This further promotes the above-described advantages while also enhancing the reliability of electrical connection between the capacitor element and the cathode lead terminal.
The above-described advantages are further promoted when the positioning groove in the upwardly bent piece of the anode lead terminal is V-shaped or U-shaped, because the anode wire can be easily fitted in the positioning groove of such a configuration.
Other objects, features and advantages of the present invention will become clearer from the description of the embodiment given below with reference to the accompanying drawings.